Grenades, Needler fire, projectiles (ie. Rocket Launcher, Fuel Rod Cannon), and vehicular charges are evaded more skillfully by the AI. Enemies go Berserk more often, and Grunts will run away for a shorter period of time, turn around, and attack again the player.

Icon: A skull marked with a smaller skull with a bruise under one eye.

Effect: Your energy shields will not recharge until you perform a melee hit on an enemy. The Energy Sword and Gravity Hammer's RT attacks count as melee attacks. The shockwave created by the Gravity Hammer will also recharge your shield. The shield down sound effect is removed as well. In addition, unlike in Halo 2, Overshields are completely nullified, and any revived characters, along with their revivers, will have only health and no shields if their shields have been wiped out. Health will not be immediately restored after reviving a teammate either. AI-controlled teammates can still recharge their shields, however.

Point Multiplier: 1.5×

Directions:

In the reactor room, go to the far left of the reactor, where there are a few ammo boxes and a pipe, clamber onto the pipe.

Walk all the way to the end of the pipe, which will lead you to a small, dark room. Be careful of Covenant forces from below and to the right, though, especially on Heroic or Legendary.

On the floor there should be a breakable piece of ground. Ground Pound onto it, and that should make you fall to another room.

Once inside, go towards the left, there should be a small pipe with the skull resting on it for you to pick up.

Effect: If you die while playing solo, you will respawn at the very beginning of the level. If any player dies while playing Co-op, all players will respawn to the last checkpoint. This is similar to what would happen when playing Co-op on Legendary in Halo 2, but it is slightly harsher on the players. In addition, the abilities to save from last checkpoint and manually revert to last checkpoint are disabled.

After you gain access to the Corp Scorpion and go through some arched rocks, you may see a cargo ship flying and being pursued by a Phaeton.

Shoot at the Phaeton until you destroy it.

An alternate strategy is to obtain an Spartan Laser and have another Spartan drive the Scorpion. As the Spartan Laser has hitscan properties, unlike the Scorpion's weapons, using it to destroy the Phaeton is much easier.

When you destroy the Phaeton, you will hear the Grunt Birthday Party sound effect which means the skull will appear in one of three places, shown in the video above.

Effect: Your entire Heads-Up Display is disabled. You can't see your weapon, first person arms, shield and health meters, motion tracker, or ammo/grenades. However, you can still see the sprint aiming reticle, radio tags from other characters, and the boost gauge when riding a Covenant vehicle.

Point Multiplier: 2.5×

Directions:

After entering the underground facility, you'll find a forklift which you have to climb.

Climb a bow that's next to the wall and look behind you where there is a cat walk.

Climb said cat walk and go to the end of it.

At the end, you will find a small cave where you need to crouch. Just walk inside.

Directions:
For you to get the skulls you need to destroy 5 cones in under 2 minutes.

The first of the cones is located close to the door where the level Glassed ends; after you go through it, you have to go the left where a rock ledge and a metal stairway are, you'll find the first cone next to boxes with a blanket on them.

Second cone is before you go inside the tunnel where Governor Sloan says "This is Governor Sloan broadcasting on all frequencies. People, if you are still planetside, make your way to the space elevator right now. Final shuttles are departing with or without you." There, you will find, to the right next to a set of stairs, the second cone for you to destroy.

Third is where the Prometheans destroy the bridge; next to a destroyed Warthog, you will find the third cone.

Fourth will be around the section with a yellow pillar and a few boxes.

Fifth and final cone will be next to a destroyed cargo ship and a red box covered with a blanket.

Once you have destroyed the cones, you must go to almost the end of the level where the Guardian begins throwing pulses. There, you will find the skull partially submerged into the ground, but with its top exposed for you to see.

Effect: If a Grunt is shot in the head with any headshot-capable weapon, a popping sound is heard, colorful confetti explodes out of it, and a sound clip of children cheering from the game Hurray! can be heard in the background. When the Grunt's head explodes, their backpack also usually explodes. The following weapons can trigger this effect:

When Cortana says: "The Gateway to the Forerunner Domain. You'll be the first organics to enter since the fall of the Forerunners. I admit, after the crash here, I didn't think I'd see you again." simply walk right where you can see a Guardian in the sky.

Effect: All vehicles and NPCs have twice the amount of health and shields.

Point Multiplier: 2.5×

Directions:

After you get out of the Sangheilli temple and you see the chapter name: "Hornet's Nest", you will see some dropships flying by.

Look backwards and look towards a collapsed column and begin to climb it.

Once you're in the top of it look to the left where you will see a small ceiling and now you will have to jump to reach it.

Note: You might have to do some trick jumping such as sprinting-jump-aiming-thrust forward-clamber. Being equipped with an Energy Sword is helpful, even more so if you are playing as Olympia Vale in co-op, who can jump higher and move faster than her other allies.

Effect: All AI-controlled units throw grenades more often, where applicable. It should be noted that characters will throw an unlimited amount of grenades at their enemies. The skull actually does seem to increase the number of Suicide Grunts.

Point Multiplier: 1.5×

Directions:

Once you've gained access to the Phaeton, land on the left platform of the Kraken and go through the entrance there.

Once you see a small ledge that sometimes has Jackal Snipers, turn left.

Board one of the Banshees in the hangar that you will find there, and fly it to an alcove that is somewhat hidden in the ceiling on the left.

Once in there, you will simply find the skull on the left of it, in a corner.

Effect: All enemy weaknesses and resistances double. Thus Covenant and Forerunner weapons deal more damage to shields but less to health, while UNSC weapons do less damage to shields but remarkably more to health.

Point Multiplier: 2×

Directions:

After defeating the first Warden Eternal, go to the hill that is on the right which is the tallest of them.

Icon: A skull marked with a smaller skull. The smaller skull seems to have a line between it and some dots (food). This describes the obvious traits of a famine: without teeth.

Effect: All weapons that are dropped by enemies or are scripted to spawn on the ground (e.g. near a crashed Pelican or group of dead bodies) have halved or reduced ammunition or charge. This also affects many special weapons (e.g. Open Hand). However, weapons found in cases still have the standard amount of ammo.

Effect: Enemies dodge grenades, needles, slow moving projectiles, and vehicle assaults with a greater success rate. In addition, enemies go berserk more often, and Grunts run away for a shorter period of time before turning around and again attacking the players.

Point Multiplier: 1.5×

Directions:

Method A: Go behind the Gamma Core to a Forerunner door, climb the chunks of snow that are on the right of it and walk all the way towards the crashed Pelican, then to the left you'll see some blocks of ice in them, and the Tough Luck skull. Make sure to jump, aim, boost forward, and clamber.

It is recommended to obtain the Vorpal Talon in front of and above the Alpha Core as it provides extra mobility (longer stabilizer duration, higher jump height, and an additional thruster pack use between cooldowns), which will prove useful for obtaining the skull through this method. These benefits become even more pronounced when playing as Olympia Vale due to her base attributes giving her higher jump height and movement speed.

Method B: On the Alpha Core, next to the Mantis is another path which you can go through so you can reach the crashed Pelican, jump onto the snowy ledge holding the skull, and claim the skull.

Either method requires you to watch out for enemy Covenant forces from below, including two Shade Turrets.